Comparison of four methods for assessing airway bacteriology in intubated, mechanically ventilated patients

A prospective evaluation of lower airway bacteriology from intubated, mechanically ventilated patients was performed by comparing the qualitative and quantitative recovery of bacteria using four different techniques. Twelve intubated, mechanically ventilated patients who satisfied accepted clinical criteria for the suspicion of ventilator-associated pneumonia were studied. Airway secretions were obtained from each patient by: (1) blind endotracheal aspiration (ET); (2) Accu-cath pulmonary culture catheter (Accu); (3) bronchoscopic protected specimen brush (BPSB); and (4) bronchoalveolar lavage (BAL). ET specimens were cultured semi-quantitatively (1+ to 4+) aerobically, and all other specimens were cultured quantitatively both aerobically and anaerobically. The BPSB recovered 9 organisms in > or = 10(3) colony forming units/ml, a standard number often used to indicate significant growth. Of these 9 organisms, 7 were recovered at > or = 10(3) cfu/ml by Accu, and 6 were recovered at > or = 10(4) cfu/ml by BAL. All 8 aerobic isolates recovered in > or = 10(3) cfu/ml by BPSB also were recovered by ET aspirate. Five of these were recovered in > or = 3+ semi-quantitative growth by ET aspirate. Of 30 organisms recovered in < 3+ semi-quantitative growth by ET aspirate, 28 were recovered in < 10(3) cfu/ml by BPSB, indicating a negative predictive value of 93%. Thus, it appears that these four methods provide reasonably similar qualitative and quantitative recovery of bacteria from the lower airways of intubated, mechanically ventilated patients. In addition, routine Gram's stain and semi-quantitative aerobic culture of endotracheal aspirate may provide useful information in patients with suspected ventilator-associated pneumonia.